XPIC project is delayed due to a wrong balance of XPD current value

Publication Date: 2012-07-25Views: 100Downloads: 0

Issue Description

During the link implementation of the RTN 950 XPIC link 1+0, QPSK, 7Mbps, 17GHz, achieving a XPD correct value was difficult in case of technical skills or hardware issues. Therefore, is not always easy to identify when the real problem of not achieving the XPD correct value comes because of the installation skills or a hardware defect. RTN 950 uses 5.83.03.31 version and IFX2 boards.

Alarm Information

No alarms related.

Handling Process

One recommended process to reach the calculated XPD value is:

Adjust the azimuth angle and elevation angle of the antennas at both ends to achieve required RSL. Be sure that vertical IDUs are powered off and you are aligning the antenna by using Horizontal IDUs.

Note down the RSL of Site-A (RSL1) on horizontally polarized IDU.

Power off the Horizontal Radio on Site-B.

Power on the vertically polarized ODU on Site-B.

Note down the RSL of Site-A (RSL2) on horizontally polarized IDU.

The calculated XPD (XPD = RSL2 – RSL1) should be 30 dB, if not then we have to align the feed horn to achieve the required value on site B.

Loose up the screws that hold feed horns and rotate the feed horn slightly until the signal level reaches 30 dB.

Note down the RSL of Site-B (RSL3) on Vertical polarized IDU.

Power off the vertical Radio on Site-A.

Power on the horizontally polarized ODU on Site-A.

Note down the RSL of Site-B (RSL4) on vertically polarized IDU.

The calculated XPD (XPD = RSL4 – RSL3) should be 30 dB if not then we have to align the feed horn to achieve the required value on site A.

Repeat back from Step 7.

If calculated XPD value can not be reached in both sides, then verify connections in IF cable, Vertical Horizontal wave guides feeders, Antenna or try replacing IFX2 boards.

Root Cause

By loosening up the screws that hold feed horns, minor adjustments vary the RSSI and RSL values. Theoretically, the difference in RSL between vertical and horizontal polarization is called ‘Cross Polarization Discrimination’ (XPD).
XPD value is usually determined by antenna specification. Some high XPD antenna has the XPD value up to 40 or 30 dB. If the required XPD value cannot be achieved, the received signal from opposite polarization will cause interference. Common symptoms are wrong received link ID and generation of MW-LOF alarm.

Suggestions

Every time you loose up the screws that hold feed horns, verify the current performance values in both ends, in both IFX2 slots by WebLCT or command line you can use:

:per-get-curdata-byboard:15m, bid;

bid represents the IFX2 board slot, where XPD_CUR is the current XPD value to be set accordingly.